Electrophysiology is a specialty within the field of cardiology for diagnosis and treatment of electrical abnormalities of the heart. Diagnosis is performed using electrode-bearing catheters placed within the heart chambers. Electrodes are positioned along a catheter shaft in a primarily two-dimensional array, although electrode elements spaced laterally around the catheter shaft give the array a very limited third dimension. Understandably, this third dimension is limited because of the small catheter shaft diameter required for such catheters as they are introduced into the heart via the veins and arteries of the body.
Electrical abnormalities are typically diagnosed by detecting the course of electrical activation paths along the endocardial surfaces of the heart chambers over time. To do this, the cardiologist may place several catheters within one or more chambers of the heart to get a better "picture" of this electrical activity. Sometimes this electrical activity is cyclical, i.e., repeats fairly well from heartbeat to heartbeat. In such cases, one catheter may serve to perform the diagnosis by moving the electrodes to various regions and then point-by-point comparing activation times with a reference. This reference may be the external EKG or another electrode catheter maintained in a stable position within a heart chamber.
However, certain types of electrical activity within a heart chamber are not cyclical. Examples include arterial flutter or arterial fibrillation, and ventricular tachycardia originating in scars in the wall of the ventricle that have resulted from infarcts. Such electrical activity is random from beat to beat. To analyze or "map" this type of electrical activity, the "picture" must be obtained during one beat. In other words, all the points of the map or picture must be obtained simultaneously within one-tenth of a second.
One solution to improve mapping is disclosed in U.S. Pat. Nos. 4,522,212 to Gelinas et al. and 4,699,147 to Chilson et al. In these patents, a catheter has, at its distal end, multiple lead-carrying arms which extend in a three-dimensional array, each arm having an inner central rib and electrodes spaced along its length. In Chilson et al., the arms are fixed at their distal end, but free to move within an outer catheter tube at their proximal end. The lead-carrying arms may be retracted into and extended from the outer catheter tube. The distal end of the catheter is directed to the designated areas of the heart and withdrawn, with the lead-carrying arms retracted within the outer catheter tube. Once at the designated areas, the arms are extended from the outer catheter tube to form a three-dimensional shape, referred to as an "elliptical envelope."
The catheter described in Chilson et al. is able to hold a large number of electrodes in different relative positions within a heart chamber. By this means, the cardiologist can obtain a map of electrical activity in one heartbeat by recording electrical signals from all the electrodes simultaneously. This is done by analyzing the spatial and temporal relationship of the electrical signals received at the electrodes.
By rotating the catheter and/or moving it longitudinally and recording electrical signals, a series of maps or pictures can be produced. A series of such pictures provides a "moving" picture of successive heartbeats, which may be able to better define the ectopic sites of activation or other activation pathways that contribute to the malfunction. This type of information may then allow the cardiologist to intervene with another catheter to destroy that causative tissue. Such destruction of heart tissue is referred to as "ablation," which is a rapidly growing field within electrophysiology and obviates the need for maximally invasive open heart surgery.
In Chilson et al. the arms are easily moved relative to each other and hence, the shape of the elliptical envelope varies from time to time and may vary even when positioned in one place due to the pumping heart chamber or the effect of rotation. Accordingly, the spatial relationship of the electrodes is subject to variation of unknown amounts. This, in turn, imparts a high degree of uncertainty or error in any map of electrical activity produced with the use of this catheter.